Time for lesson number two in our DSLR 101 series! Our topic today? You may have heard of it, it’s a little thing called ISO.
ISO is traditionally a measure of film speed; basically how sensitive a roll of film is to light. Obviously if you’re using a DSLR you’re not using film but your camera still has ISO settings. Instead of film it’s a reference to how sensitive the camera’s image sensor is to light. ISO settings can vary greatly but most cameras have at least 100, 200, 400, 800, and 1600. The lower the number the less sensitive the sensor is to light.
Although lower ISOs are usually desirable (leave your camera on Auto settings and it’ll choose 100 or 200 most of the time) to give you clear, sharp photos there are times when a higher ISO can be useful.
Choosing a higher ISO allows you to use a higher shutter speed or smaller aperture. This is especially useful for shooting in low light, particularly shooting action in low light (for example indoor sports events or concerts). It also comes in handy in places like museums and art galleries where use of flash and/or tripods may be prohibited, or in any low light situation when you don't have a tripod available!
Higher ISOs cause a grainy effect, which, while we often want the clearest photos possible, can sometimes be desirable to create a certain look in an image.
You can choose your ISO setting in the menu of most DSLRs, check your manual if you can’t find the ISO option in yours.
Try taking the same shot at several different ISO settings so you can get a feel for what each different setting produces.
Recently we've explained some basic equipment terms so today I thought I'd continue with the beginner's guides and introduce a few basic technical terms, starting with the Big Three:
Shutter Speed. Put in 4-year-old language this is the amount of time the shutter on your camera stays open. It is therefore the length of time the image sensor (in a digital camera) or film (in an old skool camera) is exposed to light.
Photographs are, generally, captured very quickly and so shutter speeds are measured in fractions of a second. The larger the number underneath the 1 (the denominator) the faster the shutter speed.
Moving from one shutter speed to the next halves or doubles the amount of light getting in. Slow shutter speeds can be used to introduce some blurring into a photo (e.g. a blurred background) or used with a tripod to get good night time photos.
Aperture. Again, in 4-year-old language, this is the size of the opening in the lens when you take a photograph. The larger the opening the more light that gets through the lens and "hits" the image sensor or film. Aperture is measured in f-stops .
Moving one f-stop up to the next halves the amount of light getting to the lens (this is confusing as moving up f-stops gives you a larger f number, e.g. f/2.8 to f/4, but the larger numbers correspond to a smaller aperture so therefore less light gets in at higher f-stop numbers). Moving the opposite way halves the amount of light getting through.
Amateur photographers often come across aperture first in relation to depth of field. Higher f-stops create larger depth of field.
ISO. If you're an old skool film photographer you have to buy your film with different ISO ratings on it, ranging from 100 to 1600 (many digital cameras offer 3200 as well). The rating refers to the sensitivity of the film to light. Lower ISOs produce higher quality (less noisy) images so as a general rule it's best to use the lowest ISO you can get away with. High ISOs can be used for indoor shots without a flash or to deliberately introduce noise into a photo.
So, that's it in a nutshell. The best advice for beginners is simple; take some time to play around with the different ISO, aperture, and shutter speed settings on your camera. Don't be afraid of messing up just try them out and see what happens. Get comfortable with which buttons you need to press & wheels you need to twirl to change them. Aperture, ISO, & shutter speed all work together so you need to be aware that when you change one you'll need to change the others too. Now, go play & learn!
When your camera is set on automatic, making a photograph is as simple as pressing the shutter release button. Somehow, the camera magically records just the right amount of light to render an image of the scene before it. But what is really going on? How does the camera know how to do that? Read on to find out how a little knowledge about what goes into making an exposure can open up new worlds of creative possibilities. And when you have read this, and mastered these steps, you can check out picture.com to create photo books and calenders using your own pictures.
There are essentially three factors that go into making an exposure whether on film or a digital sensor. These three things are the shutter speed, the lens aperture, and the film or sensor sensitivity called ISO. Each of these things individually and taken together affect how much light from a scene is recorded. And photography is nothing if not capturing light.
Shutter speed is probably the simplest to understand. Inside your camera is a movable screen in front of the film or sensor call the "shutter." When you press the shutter release button, the camera opens the shutter and then closes it again. This controls the amount of time that light is collected. It is measured in fractions of a second from 1/8000 of a second to 30 seconds.
The aperture is a variable-sized hole inside your lens through which all light must pass before it reaches the shutter. The hole can be small ("stopped" down) or it can be large ("opened" up). The wider the opening, the more light that can be collected. Aperture size is expressed in "f-stop" (or "f-numbers") like this: f/2.8. The smaller the f-stop, the larger the aperture is. When someone says they are shooting "wide open" they are referring to the aperture in their lens being open to the largest size. And when a photographer refers to "stopping down," he means closing the aperture (setting the camera to a bigger f-stop number).
Everything in the frame is in focus.
1/320s @ f/9
Let's talk about these a minute before moving on. To record a given scene, your camera has to capture light from the scene and record it on the sensor. This is called the "exposure." You can do this by capturing as much light as possible for a short time (a wide aperture and a short shutter speed) or by capturing a little light over a longer time (a small aperture and a long shutter speed). But why on earth does this matter? Because these two simple factors give you a huge amount of creative control over the resulting image.
Shutter speed and aperture control how much light gets to the sensor. But they also control something else. Shutter speed also controls time. A very fast shutter speed will capture the briefest of moments on film, freezing action, suspending water droplets in mid-air. A very slow shutter speed will blur a mountain stream, capture star trails moving across the sky, and blur moving objects to give a powerful sense of motion.
The aperture also controls the "depth of field." This is the portion of a photograph from front to back that is in acceptably sharp focus. A very small aperture opening will keep everything in the frame from the closest flower to the furthest mountain peak in focus. But a very large aperture opening (remember, a smaller f-stop!) will keep only a slice of the photo in focus: just the eyes of a portrait remain focused while the background is thrown into beautiful blur.
Narrow depth of field.
1/60s @ f/2.8
These settings affect each other because you still need a certain amount of light to record a good exposure. So, if you widen the aperture letting in more light, you also need to shorten the shutter speed to compensate. And if you lengthen the shutter speed to let light fall onto the sensor for a longer time, you need to close down the aperture to let less light in.
Fortunately, most cameras come with Shutter Priority and Aperture Priority modes to make these computations simple for you. If you put your camera in Shutter Priority mode (often labeled "Tv"), you set the shutter speed for the effect you want and your camera will compute the correct aperture. You'll do this when you want to control how much blur is in the photo or to make sure you can freeze the action. In Aperture Priority mode ("Av"), you set the aperture and the camera will compute the correct shutter speed. Do this when you want to control how much of the photo is in focus from foreground to background, either a sliver of a portrait (large aperture, small f-number) or an entire landscape (small aperture, big f-number).
Lenses usually indicate their biggest aperture setting. Lenses that are capable of very large openings like f/2.8, f/1.8 or even larger are called "fast" lenses because they let in a lot of light enabling fast shutter speeds in low-light conditions.
The last factor is ISO sensitivity. The more sensitive your film or sensor, the less light needs to be captured to record the image. ISO sensitivity also affects noise or grain. The higher the ISO, the grainier/noisier the image will be. But higher ISO also allows you to shoot with faster shutter speeds in low light, an option that is preferred by many photographers over using a flash.
Slow shutter speed, small aperture.
1/40s @ f/20
The last thing to remember is that shutter speed, aperture, and ISO are usually expressed in numbers that indicate a halving or doubling of exposure. For example, 1/30s lets in twice the amount of light as 1/60s but half as much as 1/15s. f/4 lets in twice as much light as f/5.6 but half as much as f/2.8. And ISO 800 is twice as sensitive as ISO 400 but half as sensitive as ISO 1600. This is useful to remember if you are going fully manual and want to control all three settings yourself. For example, if you slow down the shutter speed by half, you can either decrease the aperture size to keep the same exposure (1/60s @ f/5.6 is the same as 1/30s @ f/8) or decrease the ISO while keeping the aperture constant (1/60s @ ISO 400 is the same as 1/30s @ ISO 200 with constant aperture).
Shooting in aperture priority or shutter priority modes is an easy way to take advantage of this knowledge without having to remember formulas or do any math. If you want motion blur or frozen action, go with shutter priority mode and use a long or short shutter speed. If you want to control the depth of field, use aperture priority mode and set the aperture to the smaller f-stops for narrower focus (portraits) and larger f-stops for wider focus (landscape photography).
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